The invention relates to translator circuits for accessing expanded memory locations in read only memory (ROM) and dynamic random access memory (RAM) from microprocessors originally designed to access limited electronic memory.
Many personal computers have been built around microprocessors such as Commodore-MOS Technology model 6502 or Zilog Corporation model Z80. These microprocessors are 8-bit devices whose internal architecture is set up to access 64K bytes of electronic memory, either RAM or ROM. These microprocessors are both reliable and inexpensive to incorporate into any computing or controller system. A limitation, however, in their use in the past has been that expanded memory, when used with these microprocessors, has had to be magnetic medium, such as magnetic tape or disk or the like. The writing and reading of data from such peripheral storage has always been slow.
Recent advances in manufacturing techniques has allowed the cost of electronic memory (RAM and ROM) to drop dramatically thereby making it desirable to incorporate large amounts of electronic memory into personal computers.
One drawback to incorporating large amounts of electronic memory into systems utilizing older design 8-bit microprocessors has been these microprocessors' capabilities to direct access 64K of electronic memory.
It is desirable to provide a memory management unit, as a high speed interface, between large amounts of electronic memory (ROM and RAM) and the 6502 and Z80 microprocessors or similar microprocessor units, whereby these microprocessors' ability to address only 64K of electronic memory is increased to plural units of 64K electronic memory. It is also desirable that such memory management unit operate in dual microprocessor systems.